They have the right to. Is it a good idea for the long-term though? If the issue is that the birthrate is too low and the deficit you need to make up is, say, 3

They have the right to. Is it a good idea for the long-term though? If the issue is that the birthrate is too low and the deficit you need to make up is, say, 300,000 people per year, then the numbers say you need to let in 300,000 people per year, which may be far above what a xenophobic society can assimilate (I feel like we're talking about Master of Orion 2 here btw :P)